The objective of this research project is to discover the function (s) of histamine in the mammalian organism, particularly the significance of the inducible form of histidine decarboxylase apparently present in all tissues, and of that which produces histamine continuously in brain. Histamine formation, binding, release and catabolism will be studied in vivo and in vitro under a variety of experimental conditions; an attempt will be made to correlate these findings with concomitant adaptive changes by the experimental animal. Effects of drugs on the various aspects of histamine metabolism will be studied.